Devolatilization apparatus and process

ABSTRACT

Embodiments of the invention provide an apparatus or process for devolatilization of flowable materials (such as molten polymers with entrained or dissolved solvent or unreacted monomers or comonomers) using a plate heater having heating channels, the design or operation of which heating channels maintains the flowable material above its bubble point pressure during passage through a larger first zone and then induces flashing in, or downstream of, a smaller second zone of the heating channel. The apparatus enables a higher throughput per heating channel while achieving equivalent or better devolatilization, as compared to current devolatilization apparatus.

REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional application claiming priority fromthe U.S. Provisional Patent Application No. 61/150,472, filed on Feb. 6,2009, entitled “ETHYLENE-BASED POLYMERS, METHODS OF MAKING THE SAME, ANDARTICLES PREPARED THEREFROM” the teachings of which are incorporated byreference herein, as if reproduced in full herein below.

FIELD OF THE INVENTION

This invention relates to a devolatilization apparatus comprising aplate heat exchanger, and a related process for devolatilization offlowable materials at high throughputs.

BACKGROUND OF THE INVENTION

The removal of volatile components from a flowable material, referred toas “devolatilization,” is a necessary step in several industrialprocesses, including the commercial manufacture of many polymers. Inparticular, where a polymer is produced from a solution of monomers, itis necessary to remove the solvent and unreacted monomers from the finalproduct. For example, residual monomer and volatiles must be removedfrom the polymer product in the bulk or solution polymerization ofpolystyrene, styrene/acrylonitrile copolymers (SAN), or rubber-modifiedstyrene/acrylonitrile copolymers (ABS, AES, etc.), and olefin-basedpolymers (such as polypropylene, polyethylene, olefin block copolymers,and EPDM).

The separation of the volatile components from a molten polymer solutionis generally achieved by evaporation, the process consisting of heatingthe polymer solution at a temperature higher than the boiling point ofthe volatile components and removing the evolved volatile components.One method of devolatilization involves passing the polymer solutionthrough a heat exchanger and then into a zone of reduced pressure.Suitable heat exchangers for this purpose, such as those referred to asflat plate heaters or flat plate heat exchangers, comprise amultiplicity of heated plates arranged in stacks or layers, with variousheating channels connecting the interior (into which a polymer solutionis supplied) and exterior portions of the heater for passage of thesolution to be heated and devolatilized. Improved performance isattained by placing the heater within a closed shell which is partiallyevacuated.

Previous designs of flat plate heaters have been disclosed in U.S. Pat.Nos. 3,014,702; 4,153,501; 4,421,162; 4,423,767; 4,564,063; 4,808,262;5,084,134; 5,453,158; and 5,861,474, and also in PCT publicationWO96/21836.

In order to compete in the global economy, it has become necessary toinstall polymerization plants having larger capacities (in some casesexceeding 330,000 metric tons per annum, 330 KTA). In plants of thatsize, even the most efficient conventional designs (such as thosedisclosed in U.S. Pat. No. 5,453,158) typically reach or exceed thephysical size limitations of the flat plate heaters which can beconstructed economically and operated successfully, as a practicalmatter. In particular, those conventional designs are inadequate toachieve the both the necessary degree of devolatilization and the highthroughputs of these larger plants, and therefore those heat exchangershave become the capacity-limiting component in the design ofdevolatilization apparatus for larger polymerization plants.

Thus a need exists for an improved devolatilization apparatusincorporating a plate heat exchanger having an improved heating channeldesign, which design would allow higher efficiency and throughput, whileachieving sufficiently low residual volatiles in the devolatilizedmaterial.

SUMMARY OF THE INVENTION

This invention provides a devolatilization apparatus comprising:

a supply means for supplying a pressurized flowable material comprisingat least one liquid or flowable solid, as well as at least one entrainedor dissolved volatile component, which flowable material ischaracterized by a bubble point pressure which varies with thetemperature of the flowable material,

a collection-and-volatile-separation means, and

a multiplicity of plates defining a plurality of heating channels, eachchannel having two zones comprising:

-   -   a first zone having (1) an average hydraulic radius, and (2) an        inlet adapted to receive the flowable material from the supply        means, and    -   a second zone constituting the remainder of each channel, which        second zone is adapted to receive the flowable material from the        first zone and has at least one outlet adapted to discharge the        flowable material into the collection-and-volatile-separation        means, wherein at least a portion of the second zone has a        smaller hydraulic radius than the average hydraulic radius of        the first zone, and        -   wherein the design or operation of at least some of the            heating channels is such that the pressure of the flowable            material at essentially all positions within the first zone            of those heating channels exceeds the bubble point pressure            of the flowable material.

This invention also provides a devolatilization apparatus comprising:

(a) a pump for supplying a pressurized flowable material comprising atleast one molten polymer and at least one dissolved or entrainedvolatile component, which flowable material is characterized by a bubblepoint pressure which varies with the temperature of the flowablematerial,

(b) a collection-and-volatile-separation vessel, and

(c) a multiplicity of plates defining a plurality of heating channels,each channel having a substantially uniform height and having two zonescomprising:

-   -   a first zone having (1) an average hydraulic radius, and (2) an        inlet adapted to receive the flowable material from the pump,        and    -   a second zone constituting the remainder of each channel, which        second zone is adapted to receive the flowable material from the        first zone and has at least one outlet adapted to discharge the        flowable material into the collection-and-volatile-separation        vessel, wherein at least a portion of the second zone has a        smaller hydraulic radius than the average hydraulic radius of        the first zone, and    -   wherein the design or operation of at least some of the heating        channels is such that the pressure of the flowable material at        essentially all positions within the first zone of the heating        channels exceeds the bubble point pressure of the flowable        material, and

(d) a plurality of heating elements adapted to heat at least some of theplates so as to increase the temperature of the flowable material as itflows through the heating channels.

This invention also provides a process for the devolatilization of aflowable material comprising a liquid or flowable solid, as well as atleast one entrained or dissolved volatile component, which processcomprises passing that flowable material through the devolatilizationapparatus described above while operating under devolatilizationconditions so as to separate the volatile component and produce asubstantially devolatilized product.

Further, this invention provides a method for the manufacture of apolymer from at least one monomer and optionally one or more comonomersin the presence of a supported or unsupported catalyst, wherein thepolymer being produced is dissolved or suspended within a solvent, andwherein a flowable material comprising the polymer in molten form, thesolvent, and one or more unreacted monomers or comonomers is processedto remove a majority of the solvent and unreacted monomer or comonomerfrom the molten polymer, the improvement comprising using thedevolatilization apparatus of Claim 1 to process the flowable materialso as to produce a substantially devolatilized polymer product having aresidual content of the solvent and the unreacted monomer or comonomerof less than 2000 wppm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a single heating channel useful in one embodiment of theapparatus of the invention.

FIG. 2 is a simplified, axial view of the top of a flat plate useful inthe apparatus of the invention that incorporates the heating channeldesign of FIG. 1.

FIG. 3 is a side, partial cross-sectional view showing a portion of thecircumference of a stack of flat plates taken along the section shown as3-3 in FIG. 2.

FIG. 4 is a partial isometric view of one embodiment of the apparatus ofthis invention including a stack of flat plates that incorporate theheating channel design of FIG. 2.

FIG. 5 is a schematic diagram showing various elements of one embodimentof the apparatus of this invention.

FIGS. 6A, 6B, and 6C depict three alternative embodiments of the heatingchannels useful in the apparatus of this invention.

FIG. 7 depicts a single heating channel of a flat plate heater of thetype disclosed in U.S. Pat. No. 5,453,158, which conventional heatingchannel design is used for comparison with the heating channel design ofFIGS. 1, 2, and 4.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Unless stated to the contrary, implicit from the context, or customaryin the art, all parts and percents are based on weight. For purposes ofUnited States patent practice, the contents of any patent, patentapplication, or publication referenced herein are hereby incorporated byreference in their entirety (or the equivalent US version thereof is soincorporated by reference) especially with respect to the disclosure ofsynthetic techniques, definitions (to the extent not inconsistent withany definitions provided herein) and general knowledge in the art.

Definitions

By “substantially uniform,” as used with respect to a dimension (such aswidth or height) or a cross-sectional area of zone within a heatingchannel, is meant that the same is either not converging nor divergingat all, or is converging and/or diverging by no more than ten percent ofthe average of that dimension.

“Polymer” refers to a compound prepared by polymerizing monomers,whether of the same or a different type of monomer. The generic term“polymer” embraces the terms “oligomer,” “homopolymer,” “copolymer,”“terpolymer” as well as “interpolymer.”

“Interpolymer” refers to polymers prepared by the polymerization of atleast two different types of monomers. The generic term “interpolymer”includes the term “copolymer” (which is usually employed to refer to apolymer prepared from two different monomers) as well as the term“terpolymer” (which is usually employed to refer to a polymer preparedfrom three different types of monomers). It also encompasses polymersmade by polymerizing four or more types of monomers.

“Oligomer” refers to a polymer molecule consisting of only a few monomerunits, such as a dimer, trimer, or tetramer.

“Bubble point pressure” means the highest pressure at which the firstbubble of vapor is formed at a given temperature.

“Hydraulic radius” as used with respect to a zone of a heating channel,means the ratio of (a) the cross-sectional area of a conduit in which afluid is flowing to (b) the total fluid-wetted perimeter of thatconduit.

“Flowable solid” means a material (such as a slurry or a dispersion or asuspension containing particulate solids) which although comprising somenormally solid components is flowable through the heating channels ofthe apparatus of this invention under the conditions of operation or thedesign conditions.

“Thermal-fluid” means a fluid useful to convey heat from a heatingsource, and transfer that heat by indirect heat exchange to a plate ofthe apparatus of this invention. Suitable thermal-fluids include steam,hot oils, and other thermal-fluids, such as those marketed by The DowChemical Company under the trademark “DOWTHERM.”

Devolatilization of Flowable Materials

The apparatus and process of this invention are suitable fordevolatilizing a wide variety of flowable materials, and they areparticularly suitable for devolatilizing viscous flowable materials.Suitable flowable materials include normally liquid compositions inwhich are entrained or dissolved volatile components, as well asnormally solid materials (such as polymers or food stuffs) havingentrained or dissolved volatile components, but which are flowable underthe conditions in the devolatilization apparatus. Such flowablematerials include, but are not limited to, polymeric products typicallyproduced in a solution-polymerization process or a slurry-polymerizationprocess, as well as any other flowable material comprised of (a) aliquid or flowable solid and (b) entrained or dissolved volatilecomponents.

The liquid or flowable solid content of the flowable material may be anyone or more of a variety of materials. Examples of such liquid orflowable solids include: molten polymers, proteins, methylenediisocyanates, toluene diisocyanates, cheeses, sausages, dressings,candies, chocolates, molasses, other food products, waxes, heavy oils,tars, asphalts, other construction materials (such as clay, plaster,cement or aggregate in water), tree saps, pulp, paper, soaps, liquiddetergents, biomass, adhesives, pharmaceuticals, other viscous liquids,or any combination thereof. Flowable materials also include flowablesolids (such as a slurry or a dispersion or a suspension containingparticulate solids) which although comprising some normally solidcomponents is flowable through the heating channels of the apparatus ofthis invention under the conditions of operation or the designconditions.

The apparatus and process of this invention are preferred for thedevolatilization of molten polymers, such as olefin-based polymers,vinylaromatic polymers, condensation polymers, polyols, high molecularweight epoxies, and the like. For the purpose of this invention,vinylaromatic polymers are to be understood as being all homopolymersand copolymers (including graft copolymers) of one or more vinylaromaticmonomers and blends thereof with additional polymers. Examples of suchpolymers include polystyrene, rubber modified or impact-resistantpolystyrene, styrene/acrylonitrile copolymers (including rubber-modifiedversions thereof, such as ABS or AES copolymers), and blends of theforegoing with other polymers such as polycarbonate or polyphenyleneether polymers. Preferred vinylaromatic polymers are polystyrene, impactmodified polystyrene (HIPS) and ABS.

Examples of olefin-based polymers include homopolymers and copolymers(including graft copolymers) of one or more C₂ to C₁₀ olefins, includingbut not limited to, polypropylene and other propylene-based polymers,polyethylenes and other ethylene-based polymers, and olefin blockcopolymers. Such olefin-based polymers include, but are not limited to,high density polyethylenes (HDPE), low density polyethylenes (LDPE),linear low density polyethylenes (such as the LLDPE marketed by The DowChemical Company under the trademark “DOWLEX”), enhanced polyethylenes(such as those marketed by The Dow Chemical Company under the trademark“ELITE”), metallocene-catalyzed linear or substantially linear ethylenecopolymers (such as those marketed by The Dow Chemical Company under thetrademarks “AFFINITY” and “ENGAGE” and those marketed by ExxonMobilChemical Company under the trademarks “Exact” and “Exceed”),propylene-based copolymers (such as those marketed by The Dow ChemicalCompany under the trademark “VERSIFY” and those marketed by ExxonMobilChemical Company under the trademark “Vistamaxx”), and olefin-blockcopolymers (such as those marketed by The Dow Chemical Company under thetrademark “INFUSE”), and other polyolefin elastomers (such as the EPDMmarketed by The Dow Chemical Company under the trademark “NORDEL” or“NORDEL IP”).

Other examples of polymers include various oligomers, such as theadvanced epoxy resins available from The Dow Chemical Company under thetrademark “DER”, and the novolac resins available from The Dow ChemicalCompany under the trademark “DEN.”

The molecular weights and melt index (I2, as measured by ASTM methodD-1238) of such polymers may vary widely. Examples include, but are notlimited to, ethylene-based polymers having a melt index (I2, measured byASTM method D-1238 (conditions of 190° C. and 2.16 kg)) from about 0.1to about 1000 gm/10 minutes, preferably from about 0.3 to about 200gm/10 minutes, and more preferably from about 0.5 to about 10 gm/10minutes. Further examples include, but are not limited to,propylene-based polymers having a melt index (I2, measured by ASTMmethod D-1238 (conditions of 230° C. and 2.16 kg)) from about 0.1 toabout 1000 gm/10 minutes, preferably from about 0.3 to about 200 gm/10minutes, and more preferably from about 0.5 to about 10 gm/10 minutes.

The above polymers are typically produced in a solution or slurrypolymerization reactor in which the monomers and produced polymers areentrained in a solvent. Other polymer solutions also may be made(intentionally or unintentionally) containing large or small amounts ofvolatile components. Typical volatile components include solvents (suchas aromatic or aliphatic inert diluents), as well as unreacted monomersand/or comonomers. The amount of solvent, unreacted monomers, unreactedcomonomers, and/or other volatile components to be removed from thepolymer solution may range from a large excess to a mere contaminatingamount. Molten polymers produced in solution- or slurry-polymerizationplants, even after an initial flash-devolatilization stage, oftencontain from 10 to 25 weight percent or more of dissolved or entrainedvolatile components at the point they are processed in a plate heaterdevolatilization apparatus. Typically, the amount of residual volatilecomponents remaining in the devolatilized polymer should be less thanabout 2000 wppm, preferably less than 1500 wppm, and more preferablyless than 1000 wppm, as measured by ASTM D-4526.

Depending upon the starting concentration of volatile components in theflowable material to be devolatilized, and the level of residualvolatiles that are acceptable in the devolatilized product, more thanone stage (such as two or three stages) of devolatilization apparatusmay be used. In addition, the devolatilization apparatus may be used incombination with other known devolatilization techniques, such as simpleflash-devolatilization, ionic fluid extraction, extraction using asuper-critical fluid, distillation, steam-stripping orcarbon-dioxide-stripping, either in separate devolatilization stages or(in the case, for example, of steam-stripping or carbon-dioxidestripping) in combination with the apparatus of this invention withinthe same devolatilization stage.

Description of the Apparatus

The devolatilization apparatus of the invention includes an improvedheat exchanger which allows higher flow rates of flowable materialswhile achieving both high rates of heat exchange and substantiallycomplete vaporization of the volatile components, thereby increasing thethroughput and efficiency of the heat exchanger. The plates may be madeof any suitable material but preferably are made of steel, stainlesssteel, aluminum, or other metallic material.

FIG. 1 depicts the shape of a single heating channel (12) in accordancewith one embodiment of the apparatus of this invention. The heatingchannel (12) is the space defined by the walls (30) of the surroundingplate (of which only the immediately adjacent part of one plate is shownas 40) and adjacent blocks or other plates (not shown) which define thefloor and ceiling of the channel (12). The heating channel itselfcomprises two zones, a first zone (10) which has a relatively largecross-sectional area from its inlet (14) to its outlet (16), and asecond zone (20) which has a substantially smaller cross-sectional areain at least one location between the first zone's outlet (16), which isalso the inlet (24) to the second zone, and the second zone's outlet(26). The cross-sectional area of the second zone is sized (in view ofthe operating conditions and properties of the flowable material to bedevolatilized) so as to prevent any significant flashing of the volatilecomponents from the flowable material in the first zone (10), so as tokeep the flowable material within the first zone (10) pressurized aboveits bubble point pressure and thereby enhancing the heat transferefficiency from the surrounding walls (30) of the plates forming thechannel into the polymer solution within the first zone (10). Also, thecross-sectional area of the restricted portion (or all) of the secondzone (20) is sized to cause substantial flashing, preferablysubstantially complete flashing, of the volatile components from theflowable material either within the second zone (20) itself, or morepreferably immediately downstream thereof upon exiting from the outlet(26) of the second zone (20).

The plates which define the first zone of the heating channel preferablyhave sufficient surface area in contact with the flowable material toraise its temperature to the ultimate devolatilization temperature.Because pressure on the flowable material in the first zone ismaintained above the bubble point pressure, flashing is eliminated fromthe first zone. Typically, the apparatus of the invention will bedesigned and operated such that the pressure on the flowable material atessentially all locations within the first zone is at least 2 percent,preferably at least 5 percent, more preferably at least 10 percent, andmost preferably at least 15 percent above the bubble point pressure ofthe flowable material at the highest temperature within the first zoneof the heating channel.

The height of each heating channel will typically be substantiallyuniform throughout its length—as desired for ease of manufacture andassembly of stacks of the heating plates (as shown in FIGS. 3 and 4).The height is selected along with the other dimensions of the heatingchannel and the heating elements (as shown in FIGS. 2, 3, and 4)adjacent to the heating channel to optimize the efficient transfer ofheat from those heating elements into the flowable material within theheating channel. Typically heating channels will have a substantiallyuniform height over the entire length thereof of from about 0.05 cm toabout 5 cm (0.02 to 2 inches), preferably from about 0.07 to about 2.5cm (0.03 to 1 inch), more preferably from about 0.12 to about 1.3 cm(0.05 to 0.5 inch).

The shape and cross-sectional area of the first zone (10) of the heatingchannel (12) may vary widely, provided that, under the conditions ofoperation or the design conditions, the flowable material passingthrough the first zone is maintained above its bubble point pressure atessentially all locations within the first zone. Thus, as shown in FIG.1, the shape and cross-sectional area (and the hydraulic radius) of thefirst zone (10) may be substantially uniform between its inlet (14) andits outlet (16), except for relatively short transition sections—such asthe transition sections shown as (15) at the inlet (14) and as (17) atthe outlet (16). Alternatively, the shape and cross-sectional area ofthe first zone of the heating channel may be diverging, or converging,or some combination of a plurality of sections each of which might bediverging, converging, or substantially uniform. Regardless of itsconfiguration, the average hydraulic radius of the first zone should belarger than the hydraulic radius of at least a portion of the secondzone.

The second zone (20) begins at the outlet (16) of the first zone (10)and terminates in an outlet (26) that is adapted to discharge theflowable material into a collection-and-separation vessel (not shown inFIG. 1, but shown in FIG. 5 as vessel (75)). The second zone (20) variesin length, which is typically from 0.2 percent to 40 percent, preferablyfrom about 0.5 to about 10 percent, and more preferably from about 1 toabout 5 percent, of the total length of the heating channel (12). Thecross-sectional area of the second zone (20) is smaller than thecross-sectional area of the first zone (10), both to impose a sufficientback pressure on the flowable material within the first zone (10), andto result in a rapid and dramatic flashing of the volatile componentsout of the flowable material either within the second zone (20), orpreferably immediately downstream of the outlet (26) of the second zone(20). At its narrowest point the second zone (20) typically has across-sectional area from about 0.01 to about 2 square centimeters,preferably from about 0.02 to about 1 square centimeter, and morepreferably from about 0.1 to about 0.5 square centimeters. The ratio ofthe average cross-sectional area of the first zone to thecross-sectional area of the narrowest part of the second zone istypically from about 2:1 to about 200:1, and preferably is from about5:1 to about 60:1, and more preferably is from about 10:1 to about 30:1.

The shape and cross-sectional area (and hydraulic radius) of the secondzone of the heating channel may vary, provided that the second zone issized such that, under the conditions of operation or the designconditions, (a) the flowable material passing through the first zone ismaintained at a pressure above its bubble point pressure, and (b) thepressure drop induced in the second zone will result in sufficientflashing of the volatile components from the flowable material. Thus, asshown in FIG. 1, the cross-sectional area and shape of the second zone(20) may be substantially uniform between its inlet (24) and its outlet(26), except for a short transition section (25) at the inlet (24).Alternatively, the shape and cross-sectional area of the second zone maybe converging or diverging or some combination thereof to induce thenecessary pressure drop and flash the volatile components within thesecond zone (20), or preferably at the outlet (26).

The overall length of the heating channel (12) is typically from 5 to 61cm (from 2 to 24 inches), preferably from 15 to 31 cm (from 6 to 12inches), and more preferably from 20 to 26 cm (from 8 to 10 inches). Thelength of the first zone (10) is typically from 2.5 to 51 cm (from 1 to20 inches), preferably from 12 to 31 cm (from 5 to 12 inches), and morepreferably from 17 to 25 cm (from 7 to 9.5 inches). In order to increasethe efficiency of the heat transfer from the surrounding plates into theflowable material, the first zone should constitute the majority of theheating channel. Accordingly, the ratio of the length of the first zoneto the total length of the heating channel is typically from 0.5:1 to0.998:1, preferably from 0.7:1 to 0.995:1, and more preferably from0.90:1 to 0.99:1.

For an embodiment of the apparatus designed for devolatilization ofsolvent, and unreacted monomers or comonomers from a flowable materialthat contains these volatile components entrained or dissolved in aviscous molten polymer, the average hydraulic radius of the first zone(10) may be from about 0.06 to about 1.2 centimeters (0.024 to 0.47inches), and the hydraulic radius of the most-restricted portion (orall) of the second zone (20) may be from about 0.03 to about 1.1centimeters (0.012 to 0.43 inches). The height of the heating channeltypically may be from about 0.15 to about 2.5 cm (0.06 to 1 inches),preferably from about 0.19 to about 1 cm (0.07 to 0.4 inches), and morepreferably from about 0.25 to about 0.64 cm (0.1 to 0.25 inches). Thelength of the heating channel may be from about 5 to about 61 cm (2 to24 inches); and the length of the first zone of the heating channel maybe from about 2.5 to about 51 cm (1 to 20 inches), preferably from about12 to about 28 cm (5 to 11 inches), more preferably from about 17 toabout 23 cm (7 to 9 inches). The second zone constitutes the remainderof the heating channel. Consequently, the length of the second zone ofthe heating channel typically may be from about 0.2 to about 16 cm (0.1to 6 inches), preferably from about 0.5 to about 7.6 cm (0.2 to 3inches), and more preferably from about 0.7 to about 2.6 cm (0.3 to 1inches).

The width of the heating channel is different in the first and secondzones. The width of the first zone may be from about 1.3 to about 30 cm(0.5 to 12 inches), preferably from about 2.5 to about 20 cm (1 to 8inches), and more preferably from about 3.8 to about 10 cm (1.5 to 4inches). The width of the second zone may be from about 0.12 to about 15cm (0.05 to 6 inches), preferably from about 0.2 to about 2.5 cm (0.075to 1 inch), and more preferably from about 0.25 to about 0.65 cm (0.1 to0.25 inch).

In some embodiments of this invention, the ratio of (a) the averagehydraulic radius of the first zone to (b) the hydraulic radius of theportion of the second zone having the smallest cross-sectional area isfrom about 1.05:1 to about 10:1, preferably from about 1.15:1 to about8:1, and more preferably from about 1.3:1 to about 6:1.

In one preferred embodiment, the length of the heating channel is fromabout 20 to about 26 cm (8 to 10 inches), the height of the heatingchannel is from about 0.12 to about 0.38 cm (0.05 to 0.15 inches), thelength of the first zone is from about 17 to about 24 cm (7 to 9.5inches), and the width of the first zone is substantially uniform fromabout 3.8 to about 10 cm (1.5 and 4 inches), the hydraulic radius of thefirst zone is substantially uniform at from about 0.061 to about 0.184cm (0.024 to 0.072 inches), and the length of the second zone is fromabout 0.63 to about 1.91 cm (0.25 to 0.75 inches), and the width of thesecond zone is substantially uniform from about 0.25 to about 0.64 cm(0.1 and 0.25 inches) and the second zone has a single outlet, and ahydraulic radius from about 0.04 to about 0.12 cm (0.016 to 0.047inches); and the ratio of (a) the average hydraulic radius of the firstzone to (b) the hydraulic radius of the portion of the second zonehaving the smallest cross-sectional area is from about 1.05:1 to about5:1.

The heating channels of the invention will typically be designed oroperated such that the pressure of the flowable material is decreased asit flows through the first zone of the heating channel. For a givenheating channel design, the pressure drop across the first zone willvary with the throughput and the viscosity of the flowable material,with more viscous materials experiencing higher pressure drops than lessviscous materials. For devolatilization of a molten polymer, thispressure drop across the first zone may typically be from about 50 toabout 2000 psi, preferably from about 100 to about 1800 psi, and morepreferably from about 300 to about 1500 psig. However, the pressure ateach position within the first zone should remain above the bubble pointpressure at that position in order to avoid flashing of the volatilecomponents. Typically, the pressure at essentially all positions withinthe first zone will be at least 5 percent (preferably at least 10percent, and more preferably at least 15 percent) above its bubble pointpressure at the highest temperature of the flowable material within thefirst zone.

FIG. 2 depicts a simplified, axial view of the top of a plate useful inone embodiment of the apparatus of this invention that incorporates theheating channel design of FIG. 1. The plate (40) has a plurality ofheating channels (12) which provide fluid communication between anaxially aligned chamber (60) for receiving the supply of a flowablematerial to be devolatilized from a pump (not shown in FIG. 2, but shownin FIG. 5 as pump (62)), and a collection-and-separation vessel (notshown in FIG. 2, but shown in FIG. 5 as vessel (75)) exterior to andsurrounding the plate (40). Plate (40) has a plurality of heatingelements (50) disposed within the plate (40) and spaced around andbetween heating channels (12), and adapted to transfer heat from theheating elements (50) through the walls (30) of the plate (40) and intothe heating channels (12). The heating elements (50) may be any type ofheating element, such as electrical heating elements or thermal-fluidheating elements. Preferably, heating elements (50) comprise amultiplicity of heat exchange tubes through which a thermal-fluid (suchas steam, hot oil, a synthetic liquid, or other heated liquid) isflowed. The type of heated fluid to be used will depend upon thetemperature and pressure requirements of the system, as is well know inthe design of heat exchangers.

FIG. 3 depicts a side, partial cross-sectional view showing a portion ofthe circumference of a stack (70) of plates (40) in one embodiment ofthe apparatus of this invention taken along the section shown as 3-3 inFIG. 2. The stack comprises a multiplicity of plates (40) in the shapeof disks stacked in alternating layers with blocks (45) of anappropriate shape and arranged so as to define the walls, floor andceiling of each channel (12) and secured so as to define a centralchamber (not shown in FIG. 3, but shown as 60 in FIGS. 2, 4 and 5) forreceiving the flowable material to be devolatilized from the supplymeans. Heating elements (50) pass through, and are adapted to transferheat into, plates (40) and blocks (45) which in turn transfer such heatthrough the walls, floors and ceilings of the heating channels (12) intothe flowable material. The heating elements (50) may be conduits orpipes through which a thermal-fluid passes. The plates (40) and blocks(45) may be secured together by the heating elements, or other securingmeans, such as bolts (not shown). The number of plates (40) and blocks(45) in the stack (70) may vary from as few as two to as many as severalthousand plates, preferably from about 10 to about 1000 plates, and morepreferably from about 100 to about 800 plates. The number of heatingchannels (12) formed by each of the plates (40) and the adjacent blocks(45) in the stack (70) may vary from as few as one to several hundredheating channels, preferably from about 2 to about 100 heating channels,and more preferably from about 20 to about 70 heating channels perplate. The total number of heating channels (12) in a given stack (70)may vary widely, from as few as 2 to 100,000 or more, preferably fromabout 2,000 to about 60,000, more preferably from about 10,000 to about50,000.

FIG. 4 is a partial isometric view of one embodiment of the plate heaterof this invention which includes a stack (70) of alternating plates (40)and blocks (45), which together define heating channels (12) for theflowable material to pass through from the central chamber (60) to theexterior of the stack. Heating elements (50), only a few of which areshown in FIG. 4, extend through the plates (40) and blocks (45) of thestack (70).

FIG. 5 is a partially schematic diagram showing in part an obliquecut-away view of one embodiment of the apparatus of this inventioncomprising the plate heater stack (70) as previously described. Theheater is mounted within and sealably attached to a shell or vessel(75). The interior of the shell (75) and the exterior of the plateheater (70) define a collection-and-volatile-separation chamber (80)which, at the conditions of operation and/or at the design conditions,would be held at, or evacuated to, a reduced pressure (typically avacuum of 1 psia or less) at which the volatile components of theflowable material are vapors at the temperature at which the flowablematerial enters the chamber (80) after passing through heating channels(12). The chamber (80) is in operative communication with avapor-evacuation system (82), such as a vacuum pump (not shown), toremove volatile components through a vapor exit (84) of vessel (75). Thevapor-evacuation system (82) will typically include a condenser (notshown) to cool and condense the vapors and other equipment (not shown),as is well known, to separate and then either recycle or otherwisedispose of the volatile components. The chamber (80) is also inoperative communication with a discharge means (86), such as a gear pump(not shown), connected to an outlet (88) of vessel (75) and adapted todischarge the devolatilized liquid or flowable solid from chamber (80).A plurality of heating elements (50), only two of which are shown inFIG. 5, extend through the plates (40) and blocks (45) transfer heatfrom a heating source (54), such as a fired heater or boiler (notshown), through the plates and blocks into the flowable material in theheating channels (12).

By way of comparison, FIG. 7 depicts a single heating channel (512) of aflat plate heater of the type disclosed in U.S. Pat. No. 5,453,158,which conventional heating channel design is considered by applicants tobe the most effective technology prior to their present invention.Heating channel (512) has three zones: a first generally converging zone(510) which is wider at its entrance (518) than its exit (530); asecond, restrictive zone (514) wherein the channel achieves a minimumwidth sufficient to cause a pressure drop across the restrictive zone(514), thereby preventing substantial flashing of the volatilecomponents while in the first zone while allowing flashing in thesecond, restrictive zone; and a third generally diverging zone (516)terminating in outlet (520). This heating channel design allows flashingof the volatile components beginning in the second zone and continuingin the third zone. U.S. Pat. No. 5,453,158 teaches that the length ofthe first zone 510) is from 5 to 20 percent of the total length of thechannel (512), the length of the second zone (514) is from 1 to 40percent of the total length of the channel (512), and the length of thethird zone (516) is from 40 to 85 percent of the total length of thechannel (512). Flat plate heaters using that heating channel design(such as a uniform 0.10 inch height, a total length of 9.0 inches, afirst converging zone having 2.8 inch wide inlet and a length of 0.6inches, a second restrictive zone having a 4.8 inch length, and a 1.9inch width, and a third diverging zone having a 3.6 inch length and anexit width of 4.2 inches) have been used in the devolatilization ofmolten polymers at rates up to about 1.23 kg per hour per channel (2.7pounds per hour per channel), but are not capable of effectivedevolatilization at any higher throughput per channel. This restrictionnecessitates very large stacks of flat plates (in some cases requiring724 plates with 60 heating slots per plate, and a total stack height of145 inches) which either imposes practical limits on the maximum size ofthe devolatilization train (such as to about 330 thousand metric tonsper annum) where a single flat plate heater/devolatilizer apparatus isused, or requires the use of redundant flat plate heater/devolatilizertrains with the attendant higher capital costs. As shown in the Examplesand Comparative Examples below, the heating channel design of thisinvention is not so limited.

FIGS. 6A, 6B, and 6C illustrate three alternative embodiments of theheating channels useful in the apparatus of this invention, wherein thesecond zone of at least some of the heating channels has a plurality ofoutlets, rather than the single outlet (26) shown in FIG. 1.

FIG. 6A depicts the shape of a single heating channel (112) of thisinvention, which is the space defined by the walls (130) of thesurrounding plate (of which only the immediately adjacent part of oneplate is shown as (140) and (142)) and adjacent blocks or other plates(not shown) which define the floor and ceiling of the channel (112). Theheating channel (112) itself consists of two zones, a first zone (110)which has a relatively large cross-sectional area from its inlet (114)to its outlet (116), and a second zone (120) having a substantiallysmaller cross-sectional area and comprising inlet (124) and two outlets(126) and (127),

FIG. 6B depicts the shape of a single heating channel (212) of thisinvention, which is the space defined by the walls (230) of thesurrounding plate (of which only the immediately adjacent part of oneplate is shown as (240), (242) and (244)), and adjacent blocks or otherplates (not shown) which define the floor and ceiling of the channel(212). The heating channel (212) itself consists of two zones, a firstzone (210) which has a relatively large cross-sectional area from itsinlet (214) to its outlet (216), and a second zone (220) having asubstantially smaller cross-sectional area and comprising inlet (224)and three outlets (226), (227) and (228),

FIG. 6C depicts the shape of a single heating channel (312) of thisinvention, which is the space defined by the walls (330) of thesurrounding plate (of which only the immediately adjacent part of oneplate is shown as (340), (342) and (344)), and adjacent blocks or otherplates (not shown) which define the floor and ceiling of the channel(312). The heating channel itself consists of two zones, a first zone(310) which has a relatively large cross-sectional area from its inlet(314) to its outlet (316), and a second zone (320) having asubstantially smaller cross-sectional area and comprising inlet (324)and three staggered outlets (326), (327) and (328), In this embodimentwith staggered outlets (326), (327), and (328), the individual streamsof liquid or flowable solid effluent from the heating channel (such asstrings of molten polymer in one embodiment) are spaced apart radiallysufficiently so that, under the conditions of operation or the designconditions, the effluent streams do not physically contact each otheruntil after substantially complete devolatilization has occurred. It isenvisioned that such staggering of the outlets may help to avoid thecommingling of effluent liquid or flowable solids from adjacent outlets,which commingling might trap volatile components between such effluentstreams that would otherwise escape. Other approaches to avoid suchimmediate contacting of the effluent from the plate heater of thisinvention (not shown) include using a stack of plates of various shapesor sizes, such as in an inverted pyramid structure (not shown), wherethe heating channel outlets of the upper plates are spaced furtherradially from the axis of the plate heater than the plates lower in theplate heater. In such an embodiment the effluent streams would descendinto the collection vessel much like the streams of water from a showerhead.

Description of the Process

Referring to FIG. 5, in the operation of one embodiment of the processof this invention, a thermal-fluid, at the appropriate temperature, ispumped from a source (54) through heating elements (50), heating thestacked plates (40) and blocks (45). Polymer solution from the pump (62)fills the central chamber (60), enters the heating channels (12), andflows outwardly through the heating channels (12) to exit into chamber(80). As a result of the high temperature of the flowable materialleaving the heating channels (12), and the reduction in pressure tobelow the bubble point pressure, the volatile components are flashed,which flashing takes place within, or preferable immediately downstreamof, the second zone (20) of the heating channels (12). The flashedvapors are removed through vapor exit (84) by vapor-evacuation system(82). The devolatilized liquid or flowable solid is collected in thebottom of chamber (80) by gravity flow and discharged through exit (88)by a collection system (86), which may be, for example, a valve, a gearpump, or an extruder (not shown). In some embodiments for the removal ofsolvents and unreacted monomers and comonomers from molten polymers,where the concentration of volatile components in the molten polymer isvery high, adequate devolatilization may require the use of more thanone apparatus of this invention operating in series to reduce thecontent of volatile components in the molten polymer in two or moresteps.

While the illustrated embodiment indicates that each channel (12) has arectangular cross section it is understood that the edges of the inletsand outlets could also be rounded. For example, in order to avoid sharpcorners in the inlets, outlets, and/or interior of the channels theedges of the plates or blocks forming the channels could be machined tohave curved (rather than sharp) transitions.

The vaporization or thermal-decomposition temperature for any particularliquid or flowable solid is either already well known or can be easilydetermined by those skilled in the art. The temperature of the flowablematerial within the heating channels should not be raised to or abovethat temperature. When the devolatilization apparatus of this inventionis used to remove volatile components (such as solvents, unreactedmonomers and/or comonomers) from molten polymers, it is typically notnecessary to heat vinylaromatic polymers above about 350° C. or to heatolefin-based polymers above about 290° C.

EXAMPLES

The following examples are provided to illustrate the surprisingperformance achievable with the apparatus and process of this invention.The examples are presented to exemplify embodiments of the invention butare not intended to limit the invention to the specific embodiments setforth. Unless indicated to the contrary, all parts and percentages areby weight. All numerical values are approximate. When numerical rangesare given, it should be understood that embodiments outside the statedranges may still fall within the scope of the invention. Specificdetails described in each example should not be construed as necessaryfeatures of the invention. Those skilled in the art are able to modelthe temperatures and pressures of any flowable material within theheating channels of the present invention, using known finite elementmodeling techniques. Suitable modeling techniques for the flowablematerials comprising molten polymers, solvents, and unreacted monomersof the Examples and Comparative Examples are described by C. G. Dumasand R. S. Dixit in their paper “Finite Element Modeling of Polymer Flowand Heat Transfer in Processing Equipment,” which was presented at theInternational Symposium on Computer Applications in Applied PolymerScience, H. Automation, Modeling and Simulation, Toronto, Canada, andpublished in ACS Symposium Series, No. 44, 521-536, 1989. The disclosureof that paper is incorporated herein by reference.

Example 1 and Comparative Example A

In Example 1 and in Comparative Example A, a flowable materialcomprising 85 weight percent of molten ethylene-octene copolymer (havinga melt index (I2) of 0.5 gm/10 minutes) and 15 weight percent ofvolatile materials (a combination of an alkane solvent, unreactedethylene and unreacted octene comonomer) is processed in two separatedevolatilization systems.

For Example 1, one embodiment of the devolatilization apparatus of thisinvention is used. The plate heater stack has twenty-seven combinationplate-and-block elements (in which the heating channels were machinedout of the combined elements) and one end-block element, and each suchcombination element has 2 heating channels. The flowable material at atemperature of 185° C. (at which temperature the flowable material has abubble point pressure of 3.9 bar gauge [57 psig]) is pumped into a flatplate heater having 54 heating channels with the configurationillustrated in FIG. 1. The dimensions of the heating channels are: auniform height of 0.25 cm (0.1 inch), a total length of 22.9 cm (9inches), a length of the first zone of 21.6 cm (8.5 inches), asubstantially uniform width of the first zone of about 5 cm (2 inches)for all except the last 1.9 cm (0.75 inches) which is machined for asmooth convergence to the inlet of the second zone, a length of thesecond zone of 1.3 cm (0.5 inches), and a substantially uniform width ofthe second zone of 0.38 cm (0.15 inches). The hydraulic radius of allexcept the last 1.9 cm (0.75 inches) of first zone is about 0.121 cm(0.0476 inches), and the hydraulic radius of the second zone is about0.076 cm (0.03 inches), for a ratio of 1.59:1. The flowable material hasa pressure of 88 bar gauge (1276 psig) at the inlet to the first zone,and a calculated pressure of 26 bar gauge (380 psig) at the inlet to thesecond zone—which pressures are both above the bubble point pressure ofthe flowable material at those locations. The flow rate through eachchannel is maintained at about 3.54 kg/hour (7.8 pounds per hour).Within the heating channel, the flowable material is heated by indirectheat exchange (from the heating elements embedded in the plates) to apeak temperature within the first zone of the heating channel of about265° C. (at which temperature the flowable material has a bubble pointpressure of 16.8 bar gauge [243 psig], which is less than the pressureof 26 bar gauge [380 psig] at the inlet to the second zone). Thecollection and vapor-separation vessel is maintained at a reducedpressure of about 20 millibar (0.29 psia). The pressure drop from theinlet to the flat plate heater to the collection and vapor-separationvessel is about 88 bar (1276 psi). The volatile materials flash from theflowable material and are separated and recovered, and the devolatilizedpolymer product is recovered. A throughput of at least 3.54 kg/hr perheating channel (7.8 pounds per hour per heating channel) can beachieved in Example 1 while producing a polymer product having less than2000 wppm of residual volatile components, as measured by ASTM D-4526.

For purposes of comparison with Example 1, Comparative Example A employsthe same flowable material and a devolatilization apparatus that issubstantially similar to Example 1, with the exception that flat plateheater has heating channels with the three-zone configuration of U.S.Pat. No. 5,453,158 as illustrated in FIG. 7. The plate heater stack hasone hundred combination plate-and-block elements (in which the heatingchannels were machined out of the combined elements) and one end-blockelement, and each such combination element has 2 heating channels. Thedimensions of the heating channels are: a uniform height of 0.25 cm (0.1inch), a total length of 22.9 cm (9 inches), a length of the firstconverging zone of 1.6 cm (0.63 inches), a length of the secondrestricted zone of 11.6 cm (4.6 inches), and a length of the thirddiverging zone of 9.7 cm (3.8 inches). The width of the inlet to thefirst converging zone is about 7 cm (2.8 inches); the width of thesecond restricted zone is essentially uniform at 5.3 cm (2.1 inches);and the width of the third diverging zone increases from 5.3 cm (2.1inches) at its inlet in two steps out to 10.8 cm (4.2 inches) at itsexit. The hydraulic radius of the first zone converges from about 0.123cm (0.048 inches) at its inlet to about 0.121 cm (0.047 inches) at itsoutlet. The hydraulic radius of the second restrictive zone issubstantially uniform at about 0.121 cm (0.047 inches) throughout itslength. The hydraulic radius of the third zone diverges from about 0.121cm (0.047 inches) at its inlet to about 0.124 cm (0.049 inches) at itsoutlet. As taught in U.S. Pat. No. 5,453,158, the flowable material isto be maintained at a substantially constant pressure (in this caseabout 48 bar gauge (697 psig) at the 200° C. peak temperature achievableby the exit of the first zone) in the first zone to avoid flashing inthe first zone (i.e., the first 1.6 cm (0.625 inches) of the heatingchannel); however, within the second, restrictive zone the flowablematerial begins flashing, which flashing continues through the thirdzone and into the chamber of collection and vapor-separation vesselwhich is maintained at a reduced pressure of about 20 millibar (0.29psia). Within the constraints of this trumpet-like, heating-channeldesign, the pressure of the flowable material at the inlet to theheating channel is about 48 bar gauge (697 psig), and the pressure dropbetween that inlet and the collection vessel is about 48 bar (697 psi).1.2 kg/hr per heating channel (2.7 pounds per hour per heating channel)is the highest flow rate achieved in this heating channel whileproducing a polymer product having less than 2000 wppm of residualvolatile components, as measured by ASTM D-4526.

Example 2 and Comparative Example B

In Example 2 and in Comparative Example B, a flowable materialcomprising 87 weight percent of molten ethylene-octene copolymer (havinga melt index (I2) of 1.0 gm/10 minutes) and 13 weight percent ofvolatile materials (a combination of an alkane solvent and unreactedethylene and octene monomers) is processed in two separatedevolatilization systems.

For Example 2, one embodiment of the devolatilization apparatus of thisinvention is used. The plate heater stack has 282 plates and 283 blocks,and each plate has 40 heating channels. The flowable material at atemperature of 208° C. (at which temperature the flowable material has abubble point pressure of 6 bar gauge [88 psig]) is pumped into a flatplate heater having 11,280 heating channels with the configurationillustrated in FIG. 1. The dimensions of the heating channels are: auniform height of 0.25 cm (0.1 inch), a total length of 22.9 cm (9inches), a length of the first zone of 21.6 cm (8.5 inches), asubstantially uniform width of the first zone of 5.1 cm (2 inches) forall except the last 1.9 cm (0.75 inches) which is machined for a smoothconvergence to the inlet of the second zone, a length of the second zoneof 1.3 cm (0.5 inches), and a substantially uniform width of the secondzone of 0.38 cm (0.15 inches). The hydraulic radius of all except thelast 1.9 cm (0.75 inches) of first zone is about 0.121 cm (0.0476inches), and the hydraulic radius of the second zone is about 0.076 cm(0.03 inches), for a ratio of 1.59:1. The flowable material has apressure of 127 bar gauge (1847 psig) at the inlet to the first zone,and a calculated pressure of 33.5 bar gauge (486 psig) at the inlet tothe second zone—which pressures are both above the bubble point pressureof the flowable material at those locations. The flow rate through eachchannel is maintained at about 5 kg/hour (11 pounds per hour). Withinthe heating channel, the flowable material is heated by indirect heatexchange (from the heating elements embedded in the plates) to a peaktemperature within the first zone of the heating channel of about 265°C. (at which temperature the flowable material has a bubble pointpressure of 16.8 bar gauge [243 psig], which is less than the pressureof 33.5 bar gauge [486 psig] at the inlet to the second zone). Thepressure in the chamber of the collection and vapor-separation vessel ismaintained at a reduced pressure of about 20 millibar (0.29 psia). Thepressure drop from the flat plate heater inlet to the collection andvapor-separation vessel is about 127 bar (1847 psi). The volatilematerials flash from the flowable material and are separated andrecovered, and the devolatilized polymer product is recovered. Athroughput of at least 5 kg/hr per heating channel (11 pounds per hourper heating channel) can be achieved in Example 2 while producing apolymer product having less than 2000 wppm of residual volatilecomponents, as measured by ASTM D-4526.

For purposes of comparison with Example 2, Comparative Example B employsthe same flowable material and a devolatilization apparatus that issimilar to Example 2, with the exception that the heating channels ofthe flat plate heater have heating channels with the three-zoneconfiguration of U.S. Pat. No. 5,453,158 as illustrated in FIG. 7. Theplate heater stack has 1068 plates and 1069 blocks, and each plate has40 heating channels. The dimensions of the heating channels are: auniform height of about 0.25 cm (0.1 inch), a total length of 22.9 cm (9inches), a length of the first converging zone of 1.6 cm (0.63 inches),a length of the second restricted zone of 11.6 cm (4.6 inches), and alength of the third diverging zone of 9.7 cm (3.8 inches). The width ofthe inlet to the first converging zone is 7 cm (2.8 inches); the widthof the second restricted zone is essentially uniform at 5.3 cm (2.1inches); and the width of the third diverging zone increases from 5.3 cm(2.1 inches) at its inlet in two steps out to 10.8 cm (4.2 inches) atits exit. The hydraulic radius of the first zone converges from about0.123 cm (0.048 inches) at its inlet to about 0.121 cm (0.047 inches) atits outlet. The hydraulic radius of the second restrictive issubstantially uniform at about 0.121 cm (0.047 inches) throughout itslength. The hydraulic radius of the third zone diverges from about 0.121cm (0.047 inches) at its inlet to about 0.124 cm (0.049 inches) at itsoutlet. As taught in U.S. Pat. No. 5,453,158, the flowable material isto be maintained at a substantially constant pressure (in this caseabout 54.8 bar gauge (795 psig) at the 208° C. peak temperatureachievable by the exit of the first zone) in the first zone to avoidflashing in the first 1.6 cm (0.63 inches) of the heating channel;however, within the second zone the flowable material begins flashing,which flashing continues through the third zone and into the chamber ofcollection and vapor-separation vessel which is maintained at a reducedpressure of about 20 millibar (0.29 psia). Within the constraints ofthis trumpet-like, heating-channel design, the pressure of the flowablematerial at the inlet to the heating channel is about 54.8 bar gauge(795 psig), and the pressure drop between that inlet and the collectionvessel is about 54.8 bar (795 psi). 1.3 kg/hr per heating channel (2.9pounds per hour per heating channel) is the highest flow rate achievedin this heating channel while producing a polymer product having lessthan 2000 wppm of residual volatile components, as measured by ASTMD-4526.

These examples show that, while producing the same level ofdevolatilization for the flowable material, the two-zone, bottle-likeheating-channel design of the apparatus of this invention (asillustrated in FIG. 1) enables a throughput per channel that issubstantially higher than achievable with the three-zone, trumpet-likeheating-channel design of U.S. Pat. No. 5,453,158 (as illustrated inFIG. 7). In some embodiments, the bottle-like heating channel design ofthis invention enables a throughput per channel that is typically 1.2 to10 times, preferably from 1.5 to 7 times, and more preferably from 2 to5 times, the throughput of a trumpet-like channel (as described in U.S.Pat. No. 5,453,158) of the same total channel length. This surprisingresult enables the design of much more efficient and less expensivedevolatilization apparatus—requiring only a fraction of the number ofplates as the U.S. Pat. No. 5,453,158 design. Alternatively, with thesame number of plates, a flat plate heater using the heating channelconfiguration of this invention could process several times as muchflowable material, resulting in a higher capacity for the same stackheight.

Examples 3 and 4, and Comparative Example C

The following table and examples further emphasize this result:

Comparative Variable Units Example C Example 3 Example 4 Production RateKTA 370 446 925 of devolatilized polymer Ethylene-based I2 0.5 0.5 0.5Polymer Volatiles wt % 10% 10% 10% Channels Total number 43,440 13,96028,960 Channels # per plate 60 40 40 Exchanger layers Total number 724349 724 Run time Hours 7884 7884 7884 Stack Height cm 368 177 368 Inches145 69.8 145 Throughput per Kg/hr/channel 1.2 4.5 4.5 heating channel

For Comparative Example C, calculations are made of a practical-maximumproduction rate (about 370 thousand metric tons per annum, KTA)achievable in a devolatilization apparatus having a flat plate heaterwith a very large (368 cm [145 inches] total stack height) of 724 layersof plates and blocks and having the trumpet-like heating channels ofU.S. Pat. No. 5,453,158. For Examples 3 and 4, similar calculations aremade to determine the size of a flat plate heater that would be capableof an equivalent devolatilization of the same polymer at higher rates,in each case using a flat plate heater having the bottle-like heatingchannels of this invention. The calculations for Example 3 show that theapparatus of this invention should be capable of a production rate (446KTA) which is about 120% of the production rate (370 KTA) of ComparativeExample C, with a stack height which is about 50% of the height of thestack in Comparative Example C. The calculations for Example 4 show thatthe apparatus of this invention should be capable of a production rate(925 KTA) which is 250% of the production rate (370 KTA) of ComparativeExample C, with a stack height which is the same as the height of thestack in Comparative Example C.

While the invention has been described with respect to a limited numberof embodiments, the specific features of one embodiment should not beattributed to other embodiments of the invention. No single embodimentis representative of all aspects of the invention. Variations andmodifications from the described embodiments exist. Finally, any numberdisclosed herein should be construed to mean approximate, regardless ofwhether the word “about” or “approximately” is used in describing thenumber. The appended claims intend to cover all those modifications andvariations as falling within the scope of the invention.

We claim:
 1. A devolatilization apparatus comprising: (a) a pump forsupplying a pressurized flowable material comprising at least one moltenpolymer and at least one dissolved or entrained volatile component,which flowable material is characterized by a bubble point pressurewhich varies with the temperature of the flowable material, (b) acollection-and-volatile-separation vessel, and (c) a multiplicity ofplates defining a plurality of heating channels, each channel having asubstantially uniform height and having two zones comprising: a firstzone having (1) an average hydraulic radius, and (2) an inlet adapted toreceive the flowable material from the pump, and a second zoneconstituting the remainder of each channel, which second zone is adaptedto receive the flowable material from the first zone and has at leastone outlet adapted to discharge the flowable material into thecollection-and-volatile-separation vessel, wherein the outlet of thesecond zone consist essentially of a smaller hydraulic radius than theaverage hydraulic radius of the first zone, and wherein the design oroperation of at least some of the heating channels is such that thepressure of the flowable material at essentially all positions withinthe first zone of those heating channels exceeds the bubble pointpressure of the flowable material, and (d) a plurality of heatingelements adapted to heat at least some of the plates so as to increasethe temperature of the flowable material as it flows through the heatingchannels.
 2. A devolatilization apparatus comprising: a supply means forsupplying a pressurized flowable material comprising at least one liquidor flowable solid, as well as at least one entrained or dissolvedvolatile component, which flowable material is characterized by a bubblepoint pressure which varies with the temperature of the flowablematerial, a means for collecting and separating volatiles, and amultiplicity of plates defining a plurality of heating channels, eachchannel having two zones comprising: a first zone having (1) an averagehydraulic radius, and (2) an inlet adapted to receive the flowablematerial from the supply means, and a second zone constituting theremainder of each channel, which second zone is adapted to receive theflowable material from the first zone and has at least one outletadapted to discharge the flowable material into thecollection-and-volatile-separation means, wherein the outlet of thesecond zone consist essentially of a smaller hydraulic radius than theaverage hydraulic radius of the first zone, and wherein the design oroperation of at least some of the heating channels is such that thepressure of the flowable material at essentially all positions withinthe first zone of those heating channels will be above the bubble pointpressure of the flowable material.
 3. The apparatus of claim 2, furthercomprising a plurality of heating elements adapted to heat the plates soas to transfer heat into, and increase the temperature of, the flowablematerial as it flows through the heating channels.
 4. The apparatus ofclaim 1, wherein the heating elements are mounted substantiallyorthogonally in, through, or adjacent to the plates, and wherein theheating elements are selected from the group consisting of electricheating elements, thermal-fluid heating elements, and combination of twoor more thereof.
 5. The apparatus of claim 1, wherein the heatingelements are adapted to heat the plates sufficiently to transfer heat tothe flowable material as it flows through each heating channel suchthat, at the conditions of operation or at design conditions, thetemperature of that flowable material will be raised to a value that is:(a) below the lowest temperature at which the molten polymer woulditself either vaporize or decompose, and (b) no less than thetemperature necessary to cause flashing of the volatile components fromthe molten polymer at a point downstream of the first zone.
 6. Theapparatus of claim 1, wherein at least some of the heating channels havea single outlet.
 7. The apparatus of claim 1, wherein at least some ofthe heating channels have two or three outlets.
 8. The apparatus ofclaim 7, wherein the outlets of the second zones of at least some of theheating channels are spaced apart sufficiently such that, under theconditions of operation or the design conditions, the liquid orflowable-solid effluent from adjacent outlets will not physicallycontact each other until after substantially complete devolatilizationhas occurred.
 9. The apparatus of claim 1, wherein for at least some ofthe heating channels the hydraulic radius of its second zone is sizedsuch that, under the conditions of operation or the design conditions,the pressure of the flowable material within the first zone is at least5 percent above its bubble point pressure at the highest temperature ofthe flowable material within the first zone.
 10. The apparatus of claim1, wherein the total length of at least some of the heating channels isfrom 15 cm to 31 cm (6 to 12 inches), and the length of the first zoneof those heating channels is from 14 cm to 29 cm (5.5 to 11.5 inches).11. The apparatus of claim 1, wherein the total length of at least someof the heating channels is from 20 cm to 26 cm (8 to 10 inches), and thelength of the first zone of those heating channels is from 17 cm to 25cm (7 to 9.5 inches).
 12. The apparatus of claim 1, wherein at leastsome of the heating channels have a ratio of the length of the firstzone to the total length of the heating channel is from about 0.90:1 toabout 0.99:1.
 13. The apparatus of claim 1, wherein the ratio of (i) theaverage hydraulic radius of the first zone to (ii) the hydraulic radiusof that portion of the second zone having the smallest cross-sectionalarea is from about 1.05:1 to about 10:1.
 14. The apparatus of claim 1,wherein the first zone of at least some of the heating channels have ahydraulic radius that is substantially uniform along the length of thatfirst zone.
 15. The apparatus of claim 1, wherein the first zone of atleast some of the heating channels have a cross-sectional area thatconverges and/or diverges along the length of that first zone, or somecombination of converging, substantially uniform, and/or diverging alongthe length of that first zone.
 16. The apparatus of claim 1, wherein theheating channels and the remainder of the apparatus are designed oroperated such that: (i) the pressure of the flowable material atessentially all positions within the first zone of each heating channelis at least 5 percent above its bubble point pressure at the highesttemperature of the flowable material within the first zone, (ii) thethroughput of flowable material per heating channel is greater than 1.4kg/hr, and (iii) the flashing of volatile components induced within ordownstream of the second zone produces a separated liquid orflowable-solid product having a residual concentration of the volatilecomponents which is no greater than 2000 wppm.
 17. The apparatus ofclaim 1, wherein at least some of the heating channels are sized suchthat, under the conditions of operation or design conditions, thethroughput of flowable material per heating channel is from about 2 toabout 10 kg/hr.
 18. The apparatus of claim 1, wherein at least some ofthe heating channels are sized such that, under the conditions ofoperation or design conditions, the pressure drop between the inlet andthe outlet of the first zone of those heating channels will be at least100 psig.